Conventional street cleaning vehicles have been known for several decades and typically employ either one or more types of cleaning apparata to capture dirt and debris and deposit it into a hopper. Such conventional cleaning apparata include mechanical systems employing sweeping brushes, and air suctioning systems, both vacuum and regenerative types.
Street cleaning vehicles are typically driven on roads between job sites at normal roadway speeds of perhaps thirty to fifty miles per hour. However, during use at a job site, street cleaning vehicles must be driven at very slow speeds of perhaps about one to five miles per hour. In heavy dirt and debris, typically the travel speed is about one mile per hour, since maximum rate at which dirt and debris can be effectively cleaned from a paved surface.
Driving street cleaning vehicles at such slow speeds presents a very considerable and significant problem. The vehicle's powerplant, typically a diesel engine or a conventional gasoline engine must always run at about 1500 to 2000 r.p.m., or even more, in order to produce the necessary horsepower to power the cleaning apparatus. However, at this engine speed, even employing a special transmission having a very low first gear, a street cleaning vehicle would travel at a minimum speed of about five m.p.h., which is significantly faster than the required one mile per hour for cleaning heavy debris. Accordingly, it is common to use the street cleaning vehicle's brakes while cleaning heavy debris, in order to achieve the required low speed. However, since the street cleaning vehicle is in very low gear, the forward driving force is extremely powerful, and accordingly, brakes tend to wear out extremely quickly. Further, this can be dangerous as it is difficult to actually come to a stop quickly.
One simple possible solution to this above described problem is use a drive line reduction transmission in line with the conventional transmission in order to achieve a very low overall gear ratio. Athey Products Corporation of Wake Forest, N.C., U.S.A., manufacturers of the Mobil Sweeper line, produces such a street cleaning vehicle. It has been found however, that this street cleaning vehicle still requires braking to run slowly enough in heavy debris, and is extremely difficult to bring to a full stop. Further, drive line reduction transmissions are prohibitively expensive.
In order to overcome the dichotomy of providing sufficient power to drive the cleaning apparatus, while travelling at a sufficiently slow speed, many street cleaning vehicles use a main internal combustion engine and an auxiliary internal combustion engine. The main internal combustion engine is used with a conventional transmission to drive the street cleaning vehicle during travel between job sites and while performing its cleaning operation. The auxiliary internal combustion engine is used to power the cleaning apparatus to achieve varying and sufficient broom speeds while not affecting the vehicle's travel speed. However, such street cleaning vehicles still have the problem of not being able to travel slowly enough, especially during heavy dirt and debris removal where extremely slow speeds are required, since a conventional transmission is used. Moreover, the inclusion of a second internal combustion engine prohibitively increases the cost of the street cleaning vehicle, maintenance costs, and fuel costs.
Also known are specially designed hydraulically driven street cleaning vehicles that use a single internal combustion engine to power various hydraulic drive systems. A hydraulic variable displacement pump and a first hydraulic drive motor are used to drive the vehicle during travel between job sites and while performing its cleaning operation. A hydraulic gear pump and a second hydraulic drive motor are used to drive cleaning apparatus. Accordingly, it is possible to vary the travelling speed of the street cleaning vehicle during dirt and debris removal without affecting the power delivered to the cleaning apparatus. However, such hydraulically driven street cleaning vehicles are not built on a separate truck chassis and resultingly have a low top speed, tend to have extremely poor higher speed handling and braking characteristics, be mechanically unreliable, have high maintenance costs, and therefore are not preferred in many circumstances.
Another approach to the above described problem of providing sufficient horsepower to the cleaning apparatus while driving the street cleaning vehicle at very slow speeds is to directly drive the rear differential through a conventional transmission, and to hydraulically power the cleaning apparatus. One example of such a street cleaning vehicle is known as the "Broom Bear" owned by Elgin Sweeper Co. of Elgin, Ill. A variable displacement hydraulic piston pump is driven by the engine's driveshaft and powers the cleaning apparatus. Accordingly, the power available to the cleaning apparatus is controllable. However, the inherent problem with this design is that the engine speed must remain above about 1500 r.p.m. in order to produce sufficient horsepower to drive the vehicle and power the cleaning apparatus. Accordingly, the vehicle cannot be driven slowly enough in heavy debris without riding the brakes.
In an attempt to solve the above discussed problems associated with various types of street cleaning vehicles, Johnston Sweeper Co. of Pomona, Calif., has introduced a single internal combustion engine street cleaning vehicle built on a commercial truck chassis. This street cleaning vehicle employs a diesel engine driving a conventional transmission and rear differential arrangement. Additionally, a switching gearbox is installed in-line between the transmission and the conventional single input rear differential. For travel between job sites, the internal combustion engine drives the rear wheels through the transmission, the main "straight-through" input of the switching gearbox, and rear differential, essentially as if the switching gearbox had not replaced the conventional axle. A power take-off unit is operatively mounted on the transmission, with a hydraulic variable displacement pump and a hydraulic gear pump driven by the power take-off unit. The hydraulic variable displacement pump powers a first hydraulic drive motor operatively coupled to the auxiliary input of the switching gearbox, as opposed to being coupled to the main "straight-through" input. During cleaning, the switching gearbox is driven by the first hydraulic drive motor, not directly by the vehicle's engine through the conventional driveshaft. In any event, the output of the switching gearbox directly drives the one input of the rear differential.
Even through limited use, it has become readily apparent that this single internal combustion engine street cleaning vehicle has not been gaining market acceptance, mainly due to the fact that switching gear boxes tend to be prohibitively expensive, representing a significant cost relative to the cost of the entire street cleaning vehicle, which is highly undesirable.
It is an object of the present invention to provide a single internal combustion engine street cleaning vehicle.
It is another object of the present invention to provide a single internal combustion engine street cleaning vehicle that has a short wheelbase.
It is yet another object of the present invention to provide a single internal combustion engine street cleaning vehicle that can be driven at appropriately slow speeds while cleaning heavy debris and make available sufficient power for the cleaning apparatus.
It is yet another object of the present invention to provide a single internal combustion engine street cleaning vehicle that is inherently less expensive to produce than prior art models.